1. Field of the Invention
The present invention relates to a photoelectric converting film stack type solid-state image pickup device in which a plurality of photoelectric converting films that generate charges corresponding to the amount of received light are stacked on a semiconductor substrate, and more particularly to a photoelectric converting film stack type solid-state image pickup device in which the number of production steps is decreased, the performance is improved, and the production cost is reduced, and a method of producing such a device.
2. Description of the Related Art
In a CCD solid-state image pickup device or a CMOS solid-state image pickup device which is mounted on a digital camera, a large number of photoelectric converting elements (photodiodes) serving as light receiving portions, and signal read circuits which read out photoelectric conversion signals obtained in the photoelectric converting elements are formed on the surface of a semiconductor substrate. The signal read circuits are configured by, in the case of a CCD device, charge transfer circuits and transfer electrodes, or by, in the case of a CMOS device, MOS transistor circuits and signal lines.
In the related-art solid-state image pickup device, therefore, many light receiving portions and signal read circuits must be formed on the same surface of a semiconductor substrate, thereby producing a problem in that the area for the light receiving portions cannot be increased.
The related-art single-type solid-state image pickup device has a configuration in which one of color filters of, for example, red (R), green (G), and blue (B) is stacked on each of light receiving portions, so that the light receiving portion detects a light signal of the one color. In the position of a light receiving portion which detects light of, for example, red, therefore, blue and green signals are obtained by interpolating detection signals of surrounding light receiving portions which detect blue light and green light, respectively. This causes a false color, and reduces the resolution. Furthermore, blue light and green light incident on a light receiving portion where a red color filter is formed do not contribute to photoelectric conversion, but are absorbed as heat into the color filter, thereby producing another problem in that the light use efficiency is poor and the sensitivity is low.
As described above, the related-art solid-state image pickup device has various problems. On the other hand, in such a device, the number of pixels is advancing. At present, a large number or several millions of pixels or light receiving portions are integrated on one chip of a semiconductor substrate, and the size of an opening of each of the light receiving portions is near the order of the wavelength. Consequently, a CCD device and a CMOS device are hardly expected to configure an image sensor which can solve the above-discussed problems, and which is superior in image quality and sensitivity than the related-art one.
Therefore, attention is again paid to the structure of a solid-state image pickup device which is disclosed in, for example, JP-A-58-103165. The solid-state image pickup device has a structure where a red-detection photosensitive layer, a green-detection photosensitive layer, and a blue-detection photosensitive layer are stacked by a film growth technique on a semiconductor substrate in which signal read circuits are formed on the surface, these photosensitive layers are used as light receiving portions, and photoelectric conversion signals obtained in the photosensitive layers are supplied to the outside by the signal read circuits. Namely, the solid-state image pickup device has a structure of a photoelectric converting film stack type.
In this structure, it is not required to dispose the light receiving portions on the surface of the semiconductor substrate. Therefore, restrictions on the design of the signal read circuits are largely eliminated, and the light use efficiency of incident light is improved, so that the sensitivity is enhanced. Moreover, one pixel can detect light of the three primary colors or red, green, and blue. Therefore, the resolution is improved, and a false color does not occur. As a result, it is possible to solve the above-discussed problems of the related-art CCD or CMOS solid-state image pickup device.
Recently, photoelectric converting film stack type solid-state image pickup devices disclosed in JP-A-2002-83946, JP-T-2002-502120, JP-T-2003-502847 and Japanese Patent No. 3,405,099 have been proposed. An organic semiconductor or nanoparticles are used as the photosensitive layers.
When a photoelectric converting film stack type solid-state image pickup device is produced, production of a signal read circuit on the side of a semiconductor substrate is performed in the same manner as the related-art CCD or CMOS image sensor, and hence the production technique of a semiconductor device is used as it is in the production. Furthermore, also photoelectric converting films stacked on a semiconductor substrate, and electrode films and insulating films sandwiching the photoelectric converting films are easily produced by a film growing method using the printing technique, the spraying method, the vacuum depositing method, the sputtering method, the CVD method, or the like.
In a photoelectric converting film stack type solid-state image pickup device, however, it is necessary to form lines which connect a signal read circuit formed on a surface portion of a semiconductor substrate to electrode films of photoelectric converting films stacked on the circuit. Moreover, the lines must be formed as longitudinal lines which are perpendicular to the planes of the electrode films and the surface of the semiconductor substrate.
The longitudinal lines are produced in the following manner. In the related art disclosed in, for example, JP-A-2002-83946, when a photoelectric converting film is grown, longitudinal line forming portions passing through the photoelectric converting film are etched away, and conductors are buried, and, when an electrode film is formed on the photoelectric converting film, longitudinal line forming portions of the electrode film are etched away, and conductors are buried. The work is repeated several times, or at each time when a film is grown. Consequently, there arises a problem in that the number of steps of producing longitudinal lines is increased and the production cost is high.
The longitudinal lines are produced while stacking the photoelectric converting films on the semiconductor substrate. When the number of steps of producing the longitudinal lines is large, the photoelectric converting films are exposed to a high temperature during a process of producing the longitudinal lines, and therefore there is a possibility that the materials of the photoelectric converting film are deteriorated and the performance of photoelectric conversion is adversely affected. Consequently, there is also a request for reducing the number of steps of producing longitudinal lines as far as possible.
The process of producing longitudinal lines consists of repetition of, for example, application of a resist film, exposure, opening of longitudinal line portions by etching, burying of longitudinal line conductors, removal of the resist films, and polishing of the surface. When the process of producing longitudinal lines is interposed between formation of a photoelectric converting film and that of an electrode film on the photoelectric converting film, the interface between the photoelectric converting film and the electrode film is damaged by application and removal of a resist film, and polishing, and there is a possibility that the performance of photoelectric conversion is deteriorated. Because of this reason also, the number of steps of producing longitudinal lines must be reduced.